Hi there! To be perfectly honest, they’re right to a degree. I absolutely never handle my neonate GTP’s (unless moving between enclosures) until 18 months when their vertebrate have solidified and there is enough muscle tone to protect their fragile backs. As young animals, they are exactly what the pet shops have told you, they’re look but don’t touch. A number of people successfully handle their young animals with no issues at all and I don’t condemn those who do, but I just won’t take that risk.
That being said, as adult animals they are quite charming to handle, nothing makes your heart sing like a GTP tail wrapped around your pinkie. The only reason people tend to warn off handling them is:
1) The animals don’t seem to appreciate it, they like nothing more than sitting on their perch, however I handle mine occasionally for pictures and she is a lovely introductory animal for people who don’t like snakes.
2) People are obnoxiously impatient and it can take upwards of 10 minutes to coax a GTP to let their perch go. So often animals are wrenched off their branches and wind up with lower back kinks.
In short: I don’t like handling neonates. However, adults can be handled if you treat them with the gentleness they need and the respect they deserve. Patience is the key.